1. Field of the Invention
This invention relates to a hollow-fiber filter module for use in water purifiers. More particularly, it relates to a follow-fiber filter module suitable for use in water purifiers for treating relatively large volumes of water (e.g., feed water for nuclear power plants) containing metal ions and minute colloidal particles.
2. Description of the Prior Art
In conventionally known water purifiers for removing iron rust and suspended matter in water, an ultrafilter has typically been used. However, this filter is liable to clogging. Moreover, there is a limit on the size of the particles removable by such water purfiers and it is impossible to remove metal ions.
For example, steam condensate recovered from the turbines of a nuclear power plant using a boiling water reactor contains about 15 parts per billion (ppb) of impurities such as iron ions and minute colloidal particles. If this condensate is directly recycled to the reactor, the aforesaid impurities will coagulate and deposit in the reactor, causing a reduction in the efficiency of power generation. Accordingly, it is necessary to purify the condensate to an impurity concentration of about 0.5 ppb or less before recycling it to the reactor.
Where it is desired, as described above, to remove the impurities contained in steam condensate (i.e., very minute colloidal particles, metal ions and the like) with high efficiency, water purification equipment using a reverse-osmotic membrane is suitably employed in ordinary water treatment applications. However, the equipment using a reverse-osmotic membrane tends to require very high pressures for purposes of filtration and, therefore, must be large-sized. Thus, such equipment has been unsuitable for use as a filter module in the treatment of steam condensate recovered from, for example, nuclear power plants because such treatment must be carried out in a closed system.
On the other hand, porous filter membranes in the form of hollow fibers have excellent water-purifying capacity, but tend to become clogged when used in applications where it is desired to treat large volumes of water containing relatively large amounts of minute colloidal particles, metal ions and the like. Since it is difficult to rid the membrane of this clogged condition and restore its filtering function, they have seldom been used. Furthermore, in the existing state of the art concerning the treatment of circulating water for nuclear power plants, it is still desirable to develop a filter module which is practically useful not only from the viewpoint of capacity but also from the viewpoints of economy, maintenance and waste disposal.